As we say in the new issue of Entertainment Weekly hitting stands Friday, behind every man with a thirst for sex and power is an equally clever, manipulative woman… who could be played brilliantly by Natalie Dormer.

The 31-year-old Brit, who broke out Stateside in 2007 as the seductive Anne Boleyn to Jonathan Rhys Meyers’ King Henry VIII in The Tudors and now embodies King Joffrey’s shrewd betrothed Margaery Tyrell on HBO’s Game of Thrones, begins a three-episode stint tonight as Sherlock Holmes’ iconic love Irene Adler on CBS’ Elementary (through May 16’s two-hour season finale). “It’s a real privilege to be asked to play that one woman who has gotten under Sherlock’s skin,” Dormer says, noting that Elementary creator Robert Doherty was a fan of her work on the 2011 cult supernatural British TV show The Fades.

Unsure if her schedule would align with the show’s, Doherty and fellow exec producer Carl Beverly wouldn’t tell her much about the arc when they first met. “We had this kind of really amusing conversation where they were like, ‘We love you!’ And I was like, ‘I love you!’” she recalls. Though she got all the details when she officially signed on, she’s still going to be “reasonably coy” with us…

What we do know is that in this incarnation, Irene is presumed dead at the hands of Moriarty – the reason Sherlock (Jonny Lee Miller) started his downward spiral and moved to New York. We meet her in flashback and find out she worked in art restoration and met Holmes when she was asked to consult on a case. ”Occasionally, two personalities bump into each other and this mad chemical reaction happens – and not just sexual. Obviously because of the nature of Sherlock Holmes, it’s cerebral as well. He has to engage with somebody on an intellectual level to really be inspired or intoxicated by them. And the feeling is mutual,” Dormer says. “Irene brings out an entirely different side of his personality that no one else has yet been privy to. So it’s interesting to see Sherlock go through that turmoil.”

Whether this Irene Adler can be trusted remains to be seen. “God knows, because I’m the nicest person you could hope to meet,” Dormer says, when asked how she’s able to play such deliciously deceptive women. “I’m not clever enough to be in machinations and real politics. I was in D.C. for the White House Correspondents Dinner, and I know enough about my West Wing, and my Aaron Sorkin, and my House of Cards to know that I couldn’t do that in real life. So it’s just a pleasure to play something that you can really sink your teeth into.”

The transformation into Irene clicked when she began using an American accent, Dormer says, and for GoT’s Margaery, it happens when she puts on the wig. “The secret with Margaery is to play her as sincere as possible,” she says. “[For all the actors on the show], the best thing to do is switch off the part of your brain that tries to think three Chess moves in advance or about the many, many layers of subtext that are there. You just trust the writing and trust the direction, play it straight, and then this amazing alchemy happens.”

As you would expect, Dormer was happy to welcome Diana Rigg to the cast as Lady Olenna, the matriarch of House Tyrell and Margaery’s saucy grandmother. “To see her go head-to-head as a new character and prove immediately that she’s on an equal footing to Tyrion Lannister and so on and so forth is just a joy. To say, ‘Woohoo! That’s my family!’” she says, laughing. “As a veteran of the industry and as her character, it’s really great to be flanking her. It’s quite empowering.”

The two had never met before filming, but they quickly bonded. “At the end of our first day of shooting, we had a glass of wine in the hotel bar, darling. We’re British actors, thespians,” she coos. “I asked her all the questions you’d imagine I asked her: about Medea, the Tony-winning show, and about The Avengers. We just gossiped as any grandmother and granddaughter who liked each other would.”

She’s mum on GoT spoilers, but she will say that after learning Cersei is to marry Margaery’s gay brother Loras, “She’ll want to protect him as best she can from Cersei, but as we know, that will be easier said than done.” We’ve only seen the start of Margaery’s battle of wits with Cersei. “It’s going to become an incredibly dangerous and nasty rivalry as we me forward,” she says. “Hold on to your hats.”